The goal of this proposal is to investigate the principles and mechanisms whereby the central nervous system organizes the homeostasis of body temperature. By analyzing and observing the responses of single units in the preoptic anterior hypothalamus (PO/AH) and in the midbrain raphe nuclei to changes in peripheral and central temperatures and by tracing their pathways of neural communication using simultaneous stimulating and recording techniques we anticipate two tangible results. a) To understand more fully the neural basis of PO/AH thermosensitivity. b) Information on the role of the raphe in relaying afferent thermal information to the hypothalamus. Protocols for the testing of stated hypotheses in the proposal are: 1) To investigate the mechanism of PO/AH thermosensitivity by noradrenergic denervation using 6- hydroxydopamine and by altering neuronal excitability using potassium iontophoresis. 2) To investigate the influence of peripheral thermal input on the raphe nuclei and to investigate the affects of raphe stimulation on single unit activity in the PO/AH area.